Systems and methods for positioning flexible floating photobioreactors

ABSTRACT

A top reference photobioreactor system according to an embodiment of the present invention includes a flexible floating photobioreactor having a buoyancy tube filled with a gas that is less dense, and a ballast tube filled with a substance, such as saltwater, that is more dense, than the liquid in which the photobioreactor floats. A top reference photobioreactor method according to an embodiment of the present invention includes controlling a depth of the top reference photobioreactor by controlling a volume and/or density of ballast in the ballast tube and/or by controlling a volume and/or density of gas in the buoyancy tube.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional PatentApplication Ser. No. 61/313,474, filed on Mar. 12, 2010, which isincorporated by reference herein in its entirety for all purposes.

TECHNICAL FIELD

Embodiments of the present invention relate generally to bioreactors,and more specifically to floating closed bioreactor panels.

BACKGROUND

Producing biofuels, such as biodiesel, bioethanol, and/or biogasoline,from renewable energy sources provides numerous benefits. The increasingcosts, increasing difficulty of extraction, and depletion of knownfossil fuel reserves help to spur the development of such alternativefuel supplies. Efforts have been made to develop renewable energy fuelssuch as ethanol from corn grain or biodiesel from canola, palm, rapeseedand other sources. The amount of biofuel that can be derived from foodplant materials is often limited and the underlying increase in foodcommodity prices often negatively impacts food availability indeveloping countries, food prices in the developed world, on otherwiselimited food-producing land.

Efforts are underway to generate biofuels and biochemicals from non-foodmaterials, such as cellulosic ethanol from wood pulp, corn stover orsugar cane bagasse. Algae and other photosynthetic microorganisms canprovide feedstock for biofuel and biochemical synthesis. Biofuel,biochemical, and biomass production from algae could permitproductivities per unit of land area orders of magnitude higher thanthose of corn, rapeseed, palm, canola, sugar cane, and other traditionalcrops. In addition to biofuels, biochemicals and biomass can provide avariety of sustainable feedstock for plastics, chemical additives,essential human food supplements, and animal feedstock.

SUMMARY

Embodiments of the present invention include flexible and/or floatingand/or film photobioreactor panels having a buoyancy tube to permitflotation of the photobioreactor panels. Such photobioreactors mayinclude a buoyancy tube filled or partially filled with a gas, as wellas a ballast tube filled with a material that is more dense than thesurrounding fluid, to permit the flexible photobioreactor panel to befloated in a body of water while maintaining the photobioreactor panelin an upright or substantially upright configuration, in which thebuoyancy tube is at the top or at the surface or closer to the surface,and in which the ballast tube is at the bottom, or further away from thesurface.

Any known species of algae or photosynthetic or non-photosytheticmicroorganisms may be grown in a photobioreactor and utilize suchcontainment strategies according to embodiments of the presentinvention. According to some embodiments of the present inventionspecies such as but not limited to Nannochloropsis oculata,Nannochloropsis gaditana, Nannochloropsis salina, Tetraselmis suecica,Tetraselmis chuii, Nannochloropsis sp., Chlorella salina, Chlorellaprotothecoides, Chlorella ellipsoidea, Dunaliella tertiolecta,Dunaliella salina, Phaeodactulum tricomutum, Botrycoccus braunii,Chlorella emersonii, Chlorella minutissima, Chlorella pyrenoidosa,Chlorella sorokiniana, Chlorella vulgaris, Chroomonas salina, Cyclotellacryptica, Cyclotella sp., Euglena gracilis, Gymnodinium nelsoni,Haematococcus pluvialis, lsochrysis galbana, Monoraphidium minutum,Monoraphidium sp., Neochloris oleoabundans, Nitzschia laevis,Onoraphidium sp., Pavlova lutheri, Phaeodactylum tricomutum,Porphyridium cruenturn, Scenedesmus obliquuus, Scenedesmus quadricaulaScenedesmus sp., Stichococcus bacillaris, Spirulina platensis,Thalassiosira sp. may be grown, either separately or as a combination ofspecies.

A photobioreactor system according to embodiments of the presentinvention includes a reservoir containing liquid, the liquid having atop surface level, a photobioreactor, wherein the photobioreactor isflexible and is floating in the liquid, the photobioreactor including agrowth chamber containing media in which organisms may be grown, and aballast chamber containing a fluid, the fluid having an effectivedensity greater than that of the liquid, such that the ballast chamberexerts a force on the photobioreactor in a downward direction.

The photobioreactor system of any of paragraphs [0005] to [0007],wherein the fluid is a first fluid, wherein the effective density is afirst effective density, wherein the force is a first force, and whereinthe photobioreactor further includes a buoyancy chamber containing asecond fluid, the second fluid having a second effective density lessthan that of the liquid, such that the buoyancy chamber exerts a secondforce on the photobioreactor in an upward direction.

The photobioreactor system of any of paragraphs [0005] to [0008],wherein the photobioreactor further includes a sparging chamber having aplurality of holes opening into the growth chamber, the sparging chambercontaining a sparging gas or gas mixture that is configured to passthrough the plurality of holes and rise through the media.

The photobioreactor system of any of paragraphs [0005] to [0009],wherein the top surface level is a reservoir top surface level, whereinthe growth chamber comprises a head space above a media top surfacelevel, and wherein the head space accommodates accumulation of thesparging gas or gas mixture.

The photobioreactor system of any of paragraphs [0005] to [0010],wherein the buoyancy chamber is isolated from, and directly adjacent to,the head space.

The photobioreactor system of any of paragraphs [0005] to [0011],wherein the ballast chamber is isolated from, and directly adjacent to,a bottom of the growth chamber.

The photobioreactor system of any of paragraphs [0005] to [0012],wherein the sparging chamber is located at a bottom of the growthchamber, and wherein the ballast chamber is isolated from, and directlyadjacent to, the sparging chamber.

The photobioreactor system of any of paragraphs [0005] to [0013],wherein the ballast chamber and the buoyancy chamber maintain thephotobioreactor in a substantially upright position as thephotobioreactor is floating in the liquid.

The photobioreactor system of any of paragraphs [0005] to [0014],wherein the reservoir is a body of water selected from the groupconsisting of: an ocean, a lake, a sea, a pond, a river, a basin, a tub,a pool, and a tank.

The photobioreactor system of any of paragraphs [0005] to [0015],wherein the reservoir is a naturally occurring body of water.

The photobioreactor system of any of paragraphs [0005] to [0016],wherein the first fluid is salt water, and wherein the second fluid isair.

The photobioreactor system of any of paragraphs [0005] to [0017],wherein the ballast chamber comprises at least one port through whichthe fluid may be added to or removed from the ballast chamber.

The photobioreactor system of any of paragraphs [0005] to [0018],wherein the buoyancy chamber comprises at least one port through whichthe second fluid may be added to or removed from the buoyancy chamber.

The photobioreactor system of any of paragraphs [0005] to [0019],wherein the photobioreactor is one of a plurality of photobioreactorseach substantially the same as the photobioreactor, wherein theplurality of photobioreactors is floating in the liquid, and wherein theplurality of photobioreactors are positioned one next to the other suchthat a spacing between two adjacent photobioreactors of the plurality ofphotobioreactors is determined by widths of adjacent abutting ballastchambers.

The photobioreactor system of any of paragraphs [0005] to [0020],wherein each of the plurality of photobioreactors comprises a top flap,wherein the top flap is configured to be placed over a top of anadjacent photobioreactor or over the top surface level of the liquidbetween adjacent photobioreactors.

The photobioreactor system of any of paragraphs [0005] to [0021],wherein the photobioreactor is at least partially formed of asubstantially transparent plastic film.

The photobioreactor system of any of paragraphs [0005] to [0022],wherein the photobioreactor is at least partially formed of or coated byone or more anti-biofouling additives selected from the group consistingof: polyethylene glycol (PEG), hyperbranched fluoropolymer (HBFP),polyethylene (PE), polyvinyl chloride (PVC), polymethylmethacrylate(PMMA), natural rubber (NR), polydimethylsiloxane (PDMS), polystyrene(PS), perfluoropolyether (PFPE), polytetrafluoroethylene (PTFE), andsilicons and derivatives.

The photobioreactor system of any of paragraphs [0005] to [0023],wherein the media comprises one or more anti-biofouling additivesselected from the group consisting of: polyethylene glycol (PEG),silicons and derivatives, biocides, fluorocarbons, and quatinary amines.

The photobioreactor system of any of paragraphs [0005] to [0024],wherein at least a bottom surface of the ballast chamber is reinforcedto minimize possible puncture.

A method for algae growth containment according to embodiments of thepresent invention includes floating a photobioreactor in a reservoircontaining liquid, the liquid having a top surface level, wherein thephotobioreactor is flexible and comprises a growth chamber and a ballastchamber, adding media to the growth chamber, wherein the media isadapted to support a suspension culture of algae, and adding fluid tothe ballast chamber, wherein the fluid has an effective density greaterthan that of the liquid, such that the ballast chamber exerts a force onthe photobioreactor in a downward direction.

The method of paragraph [0026], wherein the fluid is a first fluid,wherein the effective density is a first effective density, wherein theforce is a first force, and wherein the photobioreactor further includesa buoyancy chamber, the method further including adding a second fluidto the buoyancy chamber, wherein the second fluid has a second effectivedensity less than that of the liquid, such that the buoyancy chamberexerts a second force on the photobioreactor in an upward direction.

The method of paragraphs [0026] or [0027], wherein the reservoir is anocean, the method further including growing the suspension culture ofalgae in the media, and mixing the suspension culture of algae byfloating the photobioreactor in a manner that permits thephotobioreactor to move in response to waves in the ocean.

The method of any of paragraphs [0026] to [0028], wherein thephotobioreactor is one of a plurality of substantially similarphotobioreactors, the method further including placing the plurality ofsubstantially similar photobioreactors in a side-by-side configurationfloating in the liquid, and adjusting a spacing between adjacentphotobioreactors by adding the fluid to, or subtracting the fluid from,the ballast chambers of adjacent photobioreactors.

The method of any of paragraphs [0026] to [0029], further includingadjusting a depth of the photobioreactor in the liquid by adding thefluid to, or subtracting the fluid from, the ballast chamber.

The method of any of paragraphs [0026] to [0030], further includingadjusting a depth of the photobioreactor in the liquid by adding thesecond fluid to, or subtracting the second fluid from, the buoyancychamber.

The method of any of paragraphs [0026] to [0031], further includingsubtracting the second fluid from the buoyancy chamber until thephotobioreactor is substantially submerged below the top surface level.

While multiple embodiments are disclosed, still other embodiments of thepresent invention will become apparent to those skilled in the art fromthe following detailed description, which shows and describesillustrative embodiments of the invention. Accordingly, the drawings anddetailed description are to be regarded as illustrative in nature andnot restrictive.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a foreshortened front side perspective view of aphotobioreactor, according to embodiments of the present invention.

FIG. 2 illustrates an enlarged partial cross-sectional view of thephotobioreactor of FIG. 1, according to embodiments of the presentinvention.

FIG. 3 illustrates an enlarged partial perspective view of an end of thephotobioreactor of FIGS. 1 and 2, according to embodiments of thepresent invention.

FIG. 4 illustrates a sectional end view of the photobioreactor of FIG.1, according to embodiments of the present invention.

FIG. 5 illustrates a row of slits that may be formed on a spargingchamber, according to embodiments of the present invention.

FIG. 6 illustrates the row of slits of FIG. 5 in a flowing condition,according to embodiments of the present invention.

FIG. 7 illustrates a sectional end view of a photobioreactor, showingsparging chamber hole placement for mixing and/or anti-fouling benefits,according to embodiments of the present invention.

FIG. 8 illustrates a sectional end view of a photobioreactor with areinforced ballast chamber bottom, according to embodiments of thepresent invention.

FIG. 9 illustrates an end view of a plurality of photobioreactors placedside-by-side, according to embodiments of the present invention.

FIG. 10 illustrates an end view of a photobioreactor with top flaps,according to embodiments of the present invention.

FIG. 11 illustrates a plurality of photobioreactors placed side-by-sidewith top flaps, according to embodiments of the present invention.

FIG. 12 illustrates an alternative photobioreactor, according toembodiments of the present invention.

FIG. 13 illustrates a partial cross-sectional perspective view ofanother alternative photobioreactor, according to embodiments of thepresent invention.

FIG. 14 illustrates a sectional end view of the photobioreactor of FIG.13, according to embodiments of the present invention.

FIG. 15 illustrates a side elevation view of the photobioreactor ofFIGS. 13 and 14, according to embodiments of the present invention.

FIG. 16 illustrates three steps for forming the photobioreactor of FIGS.13 through 15, according to embodiments of the present invention.

FIG. 17 illustrates port placement during construction of thephotobioreactor of FIGS. 13 through 15, according to embodiments of thepresent invention.

FIG. 18 illustrates a partial side elevation view of a tapered ballasttube end of a photobioreactor, according to embodiments of the presentinvention.

FIG. 19 illustrates a side elevation view of a photobioreactor depictinga harvesting procedure, according to embodiments of the presentinvention.

FIG. 20 illustrates a sectional view of a photobioreactor with dualbuoyancy chambers, according to embodiments of the present invention.

While the invention is amenable to various modifications and alternativeforms, specific embodiments have been shown by way of example in thedrawings and are described in detail below. The intention, however, isnot to limit the invention to the particular embodiments described. Onthe contrary, the invention is intended to cover all modifications,equivalents, and alternatives falling within the scope of the inventionas defined by the appended claims.

DETAILED DESCRIPTION

Researchers are exploring growing algae as a feedstock for biodiesel. Inmany designs the algae is grown inside closed bioreactors comprised ofglass or plastic, either rigid or flexible. Examples of closed systembioreactors suitable for growth of algae and other microorganisms aredescribed in U.S. Patent Application Publication No. 2008/0160591,published Jul. 3, 2008 (the “'591 Publication”), and InternationalPublication No. WO 2010/108049 A1, published on Sep. 23, 2010 (the “'049Publication”) and International Publication No. WO 2010/151606 A1,published on Dec. 29, 2010 (the “'606 Publication”), all of which areincorporated by reference herein in their entireties.

The total life cycle cost of a closed bioreactor depends on variousfactors but is generally significantly more per mass unit of biomassproduced than an open pond or reservoir, based on previous traditionalconstruction approaches and materials. Despite traditionally offeringvery high productivity, clear rigid tubes mounted on a rack in agreenhouse are often even more costly on a life cycle basis.

As described in the '591 Publication, the '049 Publication, and the '606Publication, a clear thin flexible closed clear plastic photobioreactorpanel may be suspended in a water bearing basin or reservoir tethered tothe basin bottom, for example with pipe ballast, to facilitate growthand harvest methodology improvements, resulting in significant costreduction over traditional clear rigid tube designs. As used herein, theterm “reservoir” is used in its broadest sense to refer to any body ofwater, whether large (e.g. ocean) or small (e.g. pond or tank), andwhether naturally-occurring (e.g. lake) or artificial or man-made(basin).

Embodiments of the present invention may exhibit structure and algalcontainment systems similar to those described in the '591 Publication,the '049 Publication, and the '606 Publication. Embodiments of thepresent invention may incorporate a buoyancy tube at the top and ballasttube at the bottom of the closed photobioreactor panel, which provides avery cost effective means to stably suspend the panel interrestrial-based basin water or permit deployment in a shallow or deepbody of water, lake, lagoon, or other body of water. Additionally,embodiments of the present invention include diffuse light enhancements,biofouling countermeasures, evaporation countermeasures, and gas reuseprovisions incorporated into the design in order to bundle systemenhancements into a single generational step in the technology.Additionally, a top reference panel photobioreactor system does notrequire grading or leveling of earthen surfaces, according toembodiments of the present invention.

The following is a brief description of an embodiment of a topreferenced photobioreactor 100, illustrated in FIGS. 1-4. As usedherein, the term “top reference photobioreactor” is used in its broadestsense to refer to a photobioreactor that is capable of floating inwater, and which has a buoyancy element and a ballast element. Thebuoyancy element will typically be at or near the top of thephotobioreactor, and the ballast element will typically be at or nearthe bottom of the photobioreactor, although other configurations arepossible to maintain the photobioreactor in an upright and/orsemi-upright position as it floats, according to embodiments of thepresent invention. The bioreactor 100 may include a microorganismcontainment chamber 101, which may also be referred to as a growthchamber, a buoyancy tube 102, an exhaust chamber 103 which may also bereferred to as a head space, a ballast chamber 104, a ballast chamberfill port 105, 106, a harvest/inoculation port 107, a sparge gas supplyport 108, a buoyancy chamber supply port 109, exhaust/intake ports 110,111 and/or a sparge chamber 112, according to embodiments of the presentinvention.

The photobioreactor 100 may be made from various layers of transparent,semi-transparent, reflective, semi-reflective, opaque colored,translucent colored, and/or surface treated (to create a pattern ortexture) film, selectively welded together to form the various chambers,according to embodiments of the present invention. This minimizes thecost to produce photobioreactors, which are thus flexible. FIG. 4 showsa bottom seam 408 where the two bottom edges of two layers were weldedtogether to form the bottom of the ballast chamber 104, according toembodiments of the present invention.

When the photobioreactor 100 is deployed, the photobioreactor (which maybe made from a flexible membrane or film composed of LDPE, HDPE, Nylon,Mylar, PVC, or similar material) is placed into a reservoir (e.g. abasin of water). This basin can be man-made via earthen berm or thelike, or it can be a lake, harbor or any other body of water. Thebuoyancy tube 102 is filled with gas (e.g. air, CO₂, stack gas, or thelike) to a given pressure through the buoyancy fill port 109, accordingto embodiments of the present invention. In one embodiment this tube 102is approximately 2.5″ inches diameter and is filled with gas to apressure of between 1 and 4 psi. This tube 102 may be larger or smallerin diameter depending on the size and weight of the material in theballast tube, according to embodiments of the present invention. Whenthe volume of gas in this tube 102 is buoyant enough, the buoyancy willlift the ballast tube 104 off the bottom of the water basin. Once thebuoyancy tube 102 is filled, the ports 109 connected to this tube can beplugged in order to deter any of the gas in this tube 102 from leakingout. Alternatively, the port 109 can be connected to a pressure source(accumulator, pressurized vessel, pump, blower, and the like) in orderto maintain pressure in this tube 102. If the air supply to the buoyancytube is connected via a check valve, the buoyancy tube 102 will stayinflated even if the pressure source fails, according to embodiments ofthe present invention.

The ballast tube 104 may then be filled via the ballast inlet port 105,according to embodiments of the present invention. The material orliquid that is pumped into the ballast tube 104 has a density greaterthan the water comprising the body of water in which the photobioreactorsystem 100 floats. This liquid can be a brine, sugar solution, sandslurry, and/or any other higher density liquid or gel, according toembodiments of the present invention. In some embodiments, this ballastcan be composed of a solid material (e.g. pipe, rocks, sand, concrete,and the like). In one embodiment, 2.5 lbs of salt is added to everygallon of fresh water to make a brine solution that is pumped into theballast tube 104. In another embodiment, 2.0 lbs of salt is added toevery gallon of fresh water to make a brine solution that is pumped intothe ballast tube 104.

The density of the ballast tube is approximately 1.17 kg/L while thebasin water is made of fresh water or sea water having a density betweenapproximately 1 kg/L-1.03 kg/L, according to embodiments of the presentinvention. As the ballast tube 104 is filled, the end being filled withthe ballast solution begins to sink until the film making up the algaecontainment chamber 101 is made taught, at least on one side, betweenthe ballast tube 104 and the buoyancy tube 102, according to embodimentsof the present invention. Any gas (e.g. air) that is in the ballast tube104 as it is being filled is forced to the other end of the ballast tube104, longitudinally speaking, and can be ejected from the system 100 viaa ballast port 106, according to embodiments of the present invention.Once the ballast tube 104 is filled, the one or more ballast ports 105,106 may be plugged in order to deter any of the ballast liquid fromleaking into the surrounding basin. In one embodiment, for example theembodiment shown in FIG. 9, the ballast tubes 904 a, 904 b each have adiameter of approximately six inches so that when multiple panels 900 a,900 b are placed side by side, the spacing of the panels will beapproximately six inches, and/or no less than six inches, according toembodiments of the present invention. The spacing D between adjacentphotobioreactors 900 a, 900 b will be approximately the same as thediameter of the ballast chambers 904 a, 904 b, according to embodimentsof the present invention. If the panels are packed tightly enough in thewater basin, the spacing between adjacent panels is equal to thediameter of the ballast tube, for example six inches, according toembodiments of the present invention.

According to one alternative embodiment of the present inventionillustrated in FIG. 20, a photobioreactor 2000 may include two buoyancytubes 2002, 2004. The head space 103 is located above the growth chamber101, and the sparge gas is able to pass between the buoyancy tubes 2002,2004 into the head space 103 as indicated by arrow 2006, according toembodiments of the present invention.

The microorganism containment chamber 101 may then be filled with mediathrough harvest/inoculation port 107. In one embodiment this media isdesigned for the growth of microalgae but could also be designed for thegrowth of other microorganisms such as bacteria, cyanobacteria, and thelike. The algae in this portion of the panel 101 is mixed and fed CO₂ bybubbling a CO₂ enriched gas through a sparge port 108 into the spargetube 112, which may, for example, run along an entire length of thephotobioreactor 100, according to embodiments of the present invention.The CO₂ can come from a coal fired power plant, a brewery, a cementfactory, CO₂ from air extraction devices, or similar plant that producesan enriched CO₂ gas stream. The sparge tube 112 contains smallperforations that allow the gas in the sparge tube 112 to flow into andthrough the algae/media mixture in the form of bubbles. As illustratedin FIGS. 5 and 6, these perforations can be small holes, for exampleslits 502 and/or semi-circular flaps. These bubbles travel from thesparge tube 112, located at the bottom of the algae chamber 101 to thetop of the algae chamber 101. As these bubbles travel through the media,the water contacted by these bubbles is circulated. This circulationhelps to reduce nutrient gradients in the media, circulate the algaefrom light to dark parts of the reactor, keep the algae suspended in thephotobioreactor, remove O₂, reduce thermal stratification, and the like.As illustrated in FIG. 7, if the perforations are placed toward theinner walls 706 of the growth chamber 101, at locations such as location702 and location 704, the sparge bubbles may also help to scrub and/orde-foul the inner surface of the side walls 706, in addition topotential circulation, mixing, and O₂ removal benefits.

Once the bubbles break at the free surface 113 of the media, the gasflows down the length of the exhaust tube 103 to one of the exhaustports 110, 111, according to embodiments of the present invention. Inone embodiment the exhaust tube 103 is located adjacent to the buoyancytube 102 so that as long as the buoyancy tube 102 is inflated, theexhaust tube 103 will stay above the basin water level. The pressure ofthe exhaust tube 103 may be kept at atmospheric pressure, according toembodiments of the present invention. Because of the exhaust tube 103location and pressure it does not add additional buoyant force to thephotobioreactor 100, according to embodiments of the present invention.This may help to maintain a desired panel location and/or depth in thewater. In other words, as the sparge gas flow rate is adjusted or eventurned off, the buoyancy of the panel does not change, resulting in astable panel depth in the water, according to embodiments of the presentinvention.

FIG. 4 illustrates a reservoir containing liquid 410, the liquid 410having a top surface level 402, a photobioreactor 100, wherein thephotobioreactor is flexible and is floating in the liquid 410, thephotobioreactor including a growth chamber 101 containing media in whichorganisms may be grown, and a ballast chamber 104 containing a fluid,the fluid having an effective density greater than that of the liquid410, such that the ballast chamber 104 exerts a force on thephotobioreactor 100 in a downward direction, as indicated by arrow 404.FIG. 4 also illustrates a buoyancy chamber 102 containing another fluid,for example air, such that the buoyancy chamber 102 exerts a secondforce on the photobioreactor in an upward direction, as indicated byarrow 406. These buoyancy forces help to maintain the photobioreactor100 in an upright position, as illustrated in FIG. 4, according toembodiments of the present invention.

In one embodiment (not shown), the portion of the exhaust tube 103 andthe buoyancy tube 102 located at one end of the photobioreactor 100 willexist without a ballast tube 104, or with a ballast tube of reduceddiameter, directly underneath it. FIG. 18 illustrates a ballast chamber104 having a tapered end at location 180, which is configured to provideless ballast in the region below exhaust port 111. In the event that therest of the photobioreactor becomes submerged, the accumulated spargegas will accumulate toward the end of the photobioreactor with thetapered ballast chamber 104, which will be higher in the water than therest of the photobioreactor due to having less ballast at that location.In other words, this biases that portion of the panel 100 to sit higherin the basin than the rest of the photobioreactor. Hence, if a leak wereto develop in the buoyancy tube 102 that caused the photobioreactor 100to inadvertently sink, these unballasted (or reduced ballast) ends wouldtrap air in the exhaust tube 103 behind exhaust port 111 (which isessentially the empty space, or “head space,” in the chamber 101 abovethe media free surface 113) and the panel 100 would stay above the basinwater surface, according to embodiments of the present invention.Keeping the exhaust ports 110, 111 above the basin water level minimizesor prevents the chance that basin water enters the photobioreactor, orthat media escapes into the basin water, according to embodiments of thepresent invention.

In some instances, it may be desirable to allow the photobioreactors 100to sink under the water in order to avoid damage due to inclementweather such as hail, wind storms, and the like. This can beaccomplished by evacuating some or all of the gas out of the buoyancytube 102, causing a net downward force caused by the ballast tube 104.The ballast tube 104 will then sink, for example to the bottom of thewater basin. The various ports described herein may be attached to tubesfor the addition and/or subtraction and/or flow of gases or fluids; assuch, the fluids in the ballast tube 104 and the buoyancy tube may becontrolled so as to keep the exhaust gas port 111 above the top surfacelevel of the water (or other liquid) in the reservoir in which thephotobioreactor floats, regardless of whether the rest of thephotobioreactor is being submerged or floated, according to embodimentsof the present invention.

As illustrated in FIG. 19, another instance where it may be desirable tosink the photobioreactor to the bottom of the basin is during a harvestof the media within the chamber 201. Specifically, once the gas from thebuoyancy tube 102 is evacuated causing the photobioreactor 100 to sinkto the bottom of the basin, gas can be forced into one side of the algaecontainment chamber 201 through an exhaust port 210. This will causethis side of the photobioreactor (the side opposite to the harvest port)to lift forcing the algae and media in the algae containment chambertoward the other side of the reactor where it can be extracted through aharvest/inoculation port 207, according to embodiments of the presentinvention.

A photobioreactor system according to one embodiment of the presentinvention includes a clear flexible wall integrated containment vesselset that contains a buoyancy chamber (e.g. a tube filled with air ontop), an algal broth containment chamber with an exhaust gas regionadjacent to the buoyancy chamber above the algal broth, a sparge gaschamber (e.g. a tube under the algal broth containment) and a ballastcontainment chamber at the bottom containing a material (e.g. salt andwater and/or sand and water and/or other higher mass density that flowsfor filling and makeup purposes) with a mass density in excess of freshor sea water such that when each chamber is filled to the appropriatelevel, the vessel 100 floats in the water level to the water surface andat a height commensurate with the buoyancy force's equilibrium.

Such an embodiment provides for the operation in growth mode as afloating containment. In lifted harvest mode it provides for the fillingof the algal harvest containment vessel with gas (e.g. air and/or CO2and/or N₂ and the like) starting at one end of the containment creatinga lifting of the entire vessel to a sufficient height to cause flow ofthe algal broth to the opposite end of the containment for gravity orpumped removal for harvest. In the plug flow design, it provides thesame service as the growth mode except that it can accept a periodicinflow and outflow of media and algal broth by expanding and contractingthe algal broth containment to manage the flow and maintain a floatingstable position, according to embodiments of the present invention. Sucha design eliminates or reduces the cost associated with attaching anexpensive ballast pipe to the bottom of the photobioreactor, includinglabor to assemble, attachment materials, and basin bottom flatness toensure a level panel so that exhaust flow is not impeded. Impedingexhaust flow may cause undesirable lifting of vessels and algal spillageand loss. A top reference photobioreactor may also permit non-land baseddeployments and avoidance of earthwork costs.

The buoyancy chamber can be inflated and deflated (for example by addingor subtracting the air or other gas used to fill the buoyancy chamber)to control the depth of the overall vessel 100 as well as allow it tosink below the surface 402 of the water or to the bottom of the basin orlagoon, according to embodiments of the present invention. This providesfor protection of the photobioreactor vessel 100 during inclement orstormy weather, wind, hail, snow, and the like. Submerging thephotobioreactor 100 in this fashion also facilitates a periodic cleaningof the external area which is normally exposed to air, by allowing waterto wash off accumulated debris, according to embodiments of the presentinvention.

The exhaust area 103 above the algal broth 101 is kept above the waterbasin (or similar body of water) by way of the buoyancy chamber 102,which allows the exhaust chamber 103 to maintain adequate flow area forthe exhaust gases to escape from the photobioreactor 100 withoutcreating significant back pressure due to flow losses, according toembodiments of the present invention. This placement provides for anon-obstructed containment exhaust route with minimal backpressure,according to embodiments of the present invention. Such a placementminimizes undesirable inflation and subsequent flotation of the growthchamber 101, which may cause a loss of algal broth to the connectingexhaust port 111, as well as poor sparge control and overall containmentinstability.

The exhaust discharge outlet 111 is positioned in such a way so as tostay above the external water surface 402, according to embodiments ofthe present invention. In the event of a system gas feed failure andsubsequent restart of gas feed, this configuration prevents the exhaustdischarge outlet 111 from having to be cleared of algal broth eithermanually or by a separate mechanism in order to restore exhaustfunction, according to embodiments of the present invention.

According to some embodiments of the present invention, the geometry ofsparge holes (holes made between the sparge tube 112 and the growthchamber 101) are made in a shape that causes flexing or openingexpansion during sparging to break bridging or build up around thesparge holes, to minimize biofouling flow restriction. As illustrated inFIGS. 5 and 6, such sparge holes may be slits 502 rather than roundholes, and could also be formed in other shapes, according toembodiments of the present invention. Biofouling and salts precipitationhas a tendency to build up around and over the sparge holes in somecircumstances. A slit 502 has the characteristic of flexing whenpressurized as illustrated by open slit 506 and closing when notpressurized as illustrated by closed slit 502, thus preventing back flowas well as reducing biofouling, according to embodiments of the presentinvention.

As shown in FIG. 7, sparge hole placement may be done strategically inorder to maximize mixing and provide for bubble size and velocity to beclose to the algal containment wall 706 to provide a hydrodynamicscrubbing of the wall 706, according to embodiments of the presentinvention. This may reduce or remove biofouling to the degree that itminimizes occluded light penetration into the algal broth, according toembodiments of the present invention. Embodiments of the presentinvention provide a mechanism of scrubbing with bubbles that is verycost effective compared with manual mechanical or chemical processes.

Additives to the material of the containment vessel can be used tosuppress biofouling of the algal broth, sparge gas, ballast and buoyancycontainment areas, according to embodiments of the present invention.Hydrophobic, hydrophylic, low adhesion, and/or toxic additives may beadded to the material of the containment vessel, for examplepolyethylene glycol (PEG), hyperbranched fluoropolymer (HBFP),polyethylene (PE), polyvinyl chloride (PVC), polymethylmethacrylate(PMMA), natural rubber (NR), polydimethylsiloxane (PDMS), polystyrene(PS), perfluoropolyether (PFPE), polytetrafluoroethylene (PTFE),silicons and derivatives, and the like. Corona treatment of film mayalso be used to make the surface of film more hydrophilic, according toembodiments of the present invention.

Additives to the algal broth and/or media can be employed to suppressbiofouling and foaming of the algal broth, according to embodiments ofthe present invention. Hydrophobic, hydrophylic, low adhesion, and/ortoxic additives may be added to the algal broth and/or media, forexample PEG, silicons and derivatives, biocides, fluorocarbons,quatinary amines, according to embodiments of the present invention.

Additives and surface treatments to the containment vessel surfaces canbe employed to increase light levels and optimize light distribution tomaximize growth, according to embodiments of the present invention.White surfaces, semi-reflective, tailored opaque and/or texturedsurfaces increase the diffuse light level for a given photosyntheticallyactive radiation (“PAR”) level. Algae is considerably more efficient atusing less than full sunlight to maximize growth and minimize photoinhibition. The substitution of white plastic 803 in place of the clearplastic on the ballast chamber 104 provides a curved reflective surfaceto scatter and diffuse a greater amount of light than having a clearsurface with an earthen color to the ballast, according to embodimentsof the present invention. The bottom 802 of the ballast chamber 104 mayalso be reinforced, for example with an extra layer or a thicker layer,in order to better resist puncture. The white plastic 803 may also serveto replace a white liner in the bottom of the basin to reflect light,which may reduce the cost of the lining method, according to embodimentsof the present invention.

The ballast containment 104 size and/or diameter can be made to providea mechanism for controlling the separation distance D between adjacentvessels 900 a, 900 b, as illustrated in FIG. 9. In this way, the ballasttube 104 can serve two functions, thereby reducing cost: to controllight exposure and to govern separation distance between panels,according to embodiments of the present invention.

The nature of the floating vessel enables a configuration that respondsto wave action in a basin and lagoon in the form of mixing of the algalbroth, according to embodiments of the present invention. This is a verylow cost form a energy available to mix the algal broth to increase orsustain high growth rates and reduce or eliminate sparging energyconsumption, according to embodiments of the present invention.

Various vessels 101, 102, 104 of the photobioreactor 100 can havestrategically placed reinforcing materials applied to each containmentarea and/or use thicker materials to provide the robustness to surviveinclement weather and wave action in a large body of water, lake orocean, according to embodiments of the present invention. For example,the bottom surface 802 of the ballast chamber 104 may be reinforced, asdiscussed above.

As shown in FIGS. 10 and 11, the top of the photobioreactor 100 mayinclude one or more flaps 1002, 1004, or extensions of the buoyancycontainment vessel 102, which may be constructed from either thecontainment material or some other floating plastic material that isattachable to the parent material in order to serve as a segmented coverthat overlaps the adjacent photobioreactor 100, according to embodimentsof the present invention. Alternatively, instead of overlapping anadjacent photobioreactor, such top flaps 1002, 1004 may simply cover thetop surface of the water between adjacent photobioreactors 100,according to embodiments of the present invention. Such flaps orextensions may minimize evaporation, thereby conserving water use,according to embodiments of the present invention. Such a configurationpresents a very inexpensive method for minimizing evaporation, becausethe material cost can be very low and minimal labor would be neededcompared to installation of separate covers to retain heat or minimizeevaporation. Such flaps 1002, 1004 may also be used as an alternativeway to maintain proper panel spacing, according to embodiments of thepresent invention. FIG. 11 illustrates a plurality ofadjacently-positioned photobioreactors 100 with top flaps 1002, 1004extending toward adjacent photobioreactors 100, according to embodimentsof the present invention.

FIG. 12 illustrates an alternative photobioreactor 1200, according toembodiments of the present invention. Photobioreactor 1200 includesfixed air pockets 1202 which may be welded into the side of the basicpanel material. According to some embodiments of the present invention,air cannot be inserted into or removed from the fixed air pockets 1202,so they may be formed with a small enough volume to permit the controlof the depth of the photobioreactor 1200 to be controlled based on theballast 104 volume and/or the sparge rate. Between the fixed air pockets1202 are sparge gas pockets 1204, which are areas that contain thesparge gas 1208 after it has been bubbled through the growth chamber andbefore it is exhausted, according to embodiments of the presentinvention. An exhaust opening 1206 may be formed at the top of one ormore sparge gas pockets 1204, to permit the sparge gas 1208 to exit thephotobioreactor 1200, according to embodiments of the present invention.These exhaust openings 1206 may be formed by leaving a top edge of thephotobioreactor material layers unwelded, for example. According to oneembodiment of the present invention, two or more of fixed air pockets1202 may be in fluid communication with one another.

FIG. 13 illustrates a partial cross-sectional perspective view ofanother alternative photobioreactor 200, according to embodiments of thepresent invention. Photobioreactor 200 is similar to photobioreactor100; however, photobioreactor 200 is more symmetrical, which is madepossible by a buoyancy tube which alternates along the length of thephotobioreactor 200 between a full diameter tube 142 and a set of twosmaller tubes 144, 146, one on top of the other, according toembodiments of the present invention. The head space 143 is locatedabove the buoyancy tubes 142, 144, 146, and the sparge gas from thesparge chamber 112 is permitted to pass through the buoyancy tube intothe head space 143 at the locations of the smaller-diameter buoyancytubes 144, 146, according to embodiments of the present invention. Thisbuoyancy tube with an alternating pattern may be formed by usingmultiple (e.g. four) layers of plastic liner, and placing selective weldlines across the length, both before and after folding and/oroverlapping the layers. Ink (e.g. marker ink) placed on the filmprevents welding of the layers at selected locations in order to formthe various chambers and structures, as illustrated in FIG. 16. Forexample, the welds 152 on the inside layers essentially create thedividing line between buoyancy tube 144 and buoyancy tube 146, whilewelds 153 on the outside layer essentially create the larger diameterbuoyancy tubes 142, according to embodiments of the present invention.FIG. 16 further illustrates three steps for forming the photobioreactorof FIGS. 13-15, according to embodiments of the present invention, andFIG. 17 illustrates port placement during construction of thephotobioreactor of FIGS. 13-15, according to embodiments of the presentinvention.

Various modifications and additions can be made to the exemplaryembodiments discussed without departing from the scope of the presentinvention. For example, while the embodiments described above refer toparticular features, the scope of this invention also includesembodiments having different combinations of features and embodimentsthat do not include all of the described features. Accordingly, thescope of the present invention is intended to embrace all suchalternatives, modifications, and variations as fall within the scope ofthe claims, together with all equivalents thereof.

1. A photobioreactor system comprising: a reservoir containing liquid,the liquid having a top surface level; a photobioreactor, wherein thephotobioreactor is flexible and is floating in the liquid, thephotobioreactor comprising: a growth chamber containing media in whichorganisms may be grown; a ballast chamber containing a first fluid, thefirst fluid having a first effective density greater than that of theliquid, such that the ballast chamber exerts a first force on thephotobioreactor in a downward direction; and a buoyancy chambercontaining a second fluid, the second fluid having a second effectivedensity less than that of the liquid, such that the buoyancy chamberexerts a second force on the photobioreactor in an upward direction. 2.(canceled)
 3. The photobioreactor system of claim 1, wherein thephotobioreactor further comprises: a sparging chamber having a pluralityof holes opening into the growth chamber, the sparging chambercontaining a sparging gas or gas mixture that is configured to passthrough the plurality of holes and rise through the media.
 4. Thephotobioreactor system of claim 3, wherein the top surface level is areservoir top surface level, wherein the growth chamber comprises a headspace above a media top surface level, and wherein the head spaceaccommodates accumulation of the sparging gas or gas mixture.
 5. Thephotobioreactor system of claim 4, wherein the buoyancy chamber isisolated from, and directly adjacent to, the head space.
 6. Thephotobioreactor system of claim 5, wherein the ballast chamber isisolated from, and directly adjacent to, a bottom of the growth chamber.7. The photobioreactor system of claim 5, wherein the sparging chamberis located at a bottom of the growth chamber, and wherein the ballastchamber is isolated from, and directly adjacent to, the spargingchamber.
 8. The photobioreactor system of claim 1, wherein the ballastchamber and the buoyancy chamber maintain the photobioreactor in asubstantially upright position as the photobioreactor is floating in theliquid.
 9. The photobioreactor system of claim 1, wherein the reservoiris a body of water selected from the group consisting of: an ocean, alake, a sea, a pond, a river, a basin, a tub, a pool, and a tank. 10.The photobioreactor system of claim 1, wherein the reservoir is anaturally occurring body of water.
 11. The photobioreactor system ofclaim 1, wherein the first fluid is salt water, and wherein the secondfluid is air.
 12. The photobioreactor system of claim 1, wherein theballast chamber comprises at least one port through which the firstfluid may be added to or removed from the ballast chamber.
 13. Thephotobioreactor system of claim 1, wherein the buoyancy chambercomprises at least one port through which the second fluid may be addedto or removed from the buoyancy chamber.
 14. (canceled)
 15. Thephotobioreactor system of claim 1, wherein the photobioreactor is one ofa plurality of photobioreactors each substantially the same as thephotobioreactor, wherein the plurality of photobioreactors is floatingin the liquid, and wherein the plurality of photobioreactors arepositioned one next to the other such that a spacing between twoadjacent photobioreactors of the plurality of photobioreactors isdetermined by widths of adjacent abutting ballast chambers, and whereineach of the plurality of photobioreactors comprises a top flap, whereinthe top flap is configured to be placed over a top of an adjacentphotobioreactor or over the top surface level of the liquid betweenadjacent photobioreactors.
 16. The photobioreactor system of claim 1,wherein the photobioreactor is at least partially formed of asubstantially transparent plastic film.
 17. The photobioreactor systemof claim 1, wherein the photobioreactor is at least partially formed ofor coated by an anti-biofouling additive selected from the groupconsisting of: polyethylene glycol (PEG), hyperbranched fluoropolymer(HBFP), polyethylene (PE), polyvinyl chloride (PVC),polymethylmethacrylate (PMMA), natural rubber (NR), polydimethylsiloxane(PDMS), polystyrene (PS), perfluoropolyether (PFPE),polytetrafluoroethylene (PTFE), and silicons and derivatives.
 18. Thephotobioreactor system of claim 1, wherein the media comprises ananti-biofouling additive selected from the group consisting of:polyethylene glycol (PEG), silicons and derivatives, biocides,fluorocarbons, and quatinary amines.
 19. The photobioreactor system ofclaim 1, wherein at least a bottom surface of the ballast chamber isreinforced to minimize possible puncture.
 20. A method for algae growthcontainment, comprising: floating a photobioreactor in a reservoircontaining liquid, the liquid having a top surface level, wherein thephotobioreactor is flexible and comprises a growth chamber, a ballastchamber, and a buoyancy chamber; adding media to the growth chamber,wherein the media is adapted to support a suspension culture of algae;adding a first fluid to the ballast chamber, wherein the first fluid hasa first effective density greater than that of the liquid, such that theballast chamber exerts a first force on the photobioreactor in adownward direction; and adding a second fluid to the buoyancy chamber,wherein the second fluid has a second effective density less than thatof the liquid, such that the buoyancy chamber exerts a second force onthe photobioreactor in an upward direction.
 21. (canceled)
 22. Themethod of claim 20, wherein the reservoir is an ocean, the methodfurther comprising: growing the suspension culture of algae in themedia; and mixing the suspension culture of algae by floating thephotobioreactor in a manner that permits the photobioreactor to move inresponse to waves in the ocean.
 23. The method of claim 20, wherein thephotobioreactor is one of a plurality of substantially similarphotobioreactors, the method further comprising: placing the pluralityof substantially similar photobioreactors in a side-by-sideconfiguration floating in the liquid; and adjusting a spacing betweenadjacent photobioreactors by adding the first fluid to, or subtractingthe first fluid from, the ballast chambers of adjacent photobioreactors.24. The method of claim 20, further comprising: adjusting a depth of thephotobioreactor in the liquid by adding the first fluid to, orsubtracting the first fluid from, the ballast chamber.
 25. The method ofclaim 20, further comprising: adjusting a depth of the photobioreactorin the liquid by adding the second fluid to, or subtracting the secondfluid from, the buoyancy chamber.
 26. The method of claim 25, furthercomprising: subtracting the second fluid from the buoyancy chamber untilthe photobioreactor is substantially submerged below the top surfacelevel.